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# XPathExpression

`public interface XPathExpression`
``

javax.xml.xpath.XPathExpression

`XPathExpression` provides access to compiled XPath expressions.

Evaluation of XPath Expressions.
context | If a request is made to evaluate the expression in the absence of a context item, an empty document node will be used for the context. For the purposes of evaluating XPath expressions, a DocumentFragment is treated like a Document node.
variables | If the expression contains a variable reference, its value will be found through the `XPathVariableResolver`. An `XPathExpressionException` is raised if the variable resolver is undefined or the resolver returns `null` for the variable. The value of a variable must be immutable through the course of any single evaluation.
functions | If the expression contains a function reference, the function will be found through the `XPathFunctionResolver`. An `XPathExpressionException` is raised if the function resolver is undefined or the function resolver returns `null` for the function.
QNames | QNames in the expression are resolved against the XPath namespace context.
result | This result of evaluating an expression is converted to an instance of the desired return type. Valid return types are defined in `XPathConstants`. Conversion to the return type follows XPath conversion rules.

See also:

- XML Path Language (XPath) Version 1.0, Expressions

## Summary

### Public methods
`abstract String` | `evaluate(Object item)` Evaluate the compiled XPath expression in the specified context and return the result as a `String`.
`abstract String` | `evaluate(InputSource source)` Evaluate the compiled XPath expression in the context of the specified `InputSource` and return the result as a `String`.
`abstract Object` | `evaluate(InputSource source, QName returnType)` Evaluate the compiled XPath expression in the context of the specified `InputSource` and return the result as the specified type.
`abstract Object` | `evaluate(Object item, QName returnType)` Evaluate the compiled XPath expression in the specified context and return the result as the specified type.

## Public methods

### evaluate

    public abstract String evaluate (Object item)

Evaluate the compiled XPath expression in the specified context and return the result as a `String`.

This method calls `evaluate(java.lang.Object, javax.xml.namespace.QName)` with a `returnType` of `XPathConstants#STRING`.

See Evaluation of XPath Expressions for context item evaluation, variable, function and QName resolution and return type conversion.

If a `null` value is provided for `item`, an empty document will be used for the context.

Parameters
`item` | `Object`: The starting context (node or node list, for example).

Returns
`String` | The `String` that is the result of evaluating the expression and converting the result to a `String`.

Throws
`XPathExpressionException` | If the expression cannot be evaluated.

### evaluate

    public abstract String evaluate (InputSource source)

Evaluate the compiled XPath expression in the context of the specified `InputSource` and return the result as a `String`.

This method calls `evaluate(org.xml.sax.InputSource, javax.xml.namespace.QName)` with a `returnType` of `XPathConstants#STRING`.

See Evaluation of XPath Expressions for context item evaluation, variable, function and QName resolution and return type conversion.

If `source` is `null`, then a `NullPointerException` is thrown.

Parameters
`source` | `InputSource`: The `InputSource` of the document to evaluate over.

Returns
`String` | The `String` that is the result of evaluating the expression and converting the result to a `String`.

Throws
`XPathExpressionException` | If the expression cannot be evaluated.
`NullPointerException` | If `source` is `null`.

### evaluate

    public abstract Object evaluate (InputSource source,
                    QName returnType)

Evaluate the compiled XPath expression in the context of the specified `InputSource` and return the result as the specified type.

This method builds a data model for the `InputSource` and calls `evaluate(java.lang.Object, javax.xml.namespace.QName)` on the resulting document object.

See Evaluation of XPath Expressions for context item evaluation, variable, function and QName resolution and return type conversion.

If `returnType` is not one of the types defined in `XPathConstants`, then an `IllegalArgumentException` is thrown.

If `source` or `returnType` is `null`, then a `NullPointerException` is thrown.

Parameters
`source` | `InputSource`: The `InputSource` of the document to evaluate over.
`returnType` | `QName`: The desired return type.

Returns
`Object` | The `Object` that is the result of evaluating the expression and converting the result to `returnType`.

Throws
`XPathExpressionException` | If the expression cannot be evaluated.
`IllegalArgumentException` | If `returnType` is not one of the types defined in `XPathConstants`.
`NullPointerException` | If `source` or `returnType` is `null`.

### evaluate

    public abstract Object evaluate (Object item,
                    QName returnType)

Evaluate the compiled XPath expression in the specified context and return the result as the specified type.

See Evaluation of XPath Expressions for context item evaluation, variable, function and QName resolution and return type conversion.

If `returnType` is not one of the types defined in `XPathConstants`, then an `IllegalArgumentException` is thrown.

If a `null` value is provided for `item`, an empty document will be used for the context. If `returnType` is `null`, then a `NullPointerException` is thrown.

Parameters
`item` | `Object`: The starting context (node or node list, for example).
`returnType` | `QName`: The desired return type.

Returns
`Object` | The `Object` that is the result of evaluating the expression and converting the result to `returnType`.

Throws
`XPathExpressionException` | If the expression cannot be evaluated.
`IllegalArgumentException` | If `returnType` is not one of the types defined in `XPathConstants`.
`NullPointerException` | If `returnType` is `null`.

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